1. Field of the Invention
The present invention relates to a video signal processing apparatus and a video signal processing method which are suitable for a scanning line interpolation circuit, etc. configured to convert scanning lines from a video signal of an interlaced mode to a video signal of a progressive mode.
2. Description of the Related Art
A plasma display apparatus, a liquid crystal display apparatus, etc. configure a matrix display apparatus in which pixels are placed in a matrix state corresponding to intersecting points of a plurality of scanning lines and data lines. In the matrix display apparatus, video information per pixel is sequentially displayed for every scanning line so that an image is displayed.
Some of such matrix display apparatuses have a display screen whose resolution is higher than the resolution of an input video signal. In such a case, a scanning line interpolation circuit may be adopted which improves the image quality by setting a interpolation line between scanning lines based on inputted video signals, and generating interpolation pixels on the interpolation line.
Some scanning line interpolation circuit may generate the interpolation pixel according to an average value of pixels of upper and under lines of the interpolation line. However, this interpolation method may generate such an image that a diagonal line looks as jagging, what we say, jaggy is conspicuous in some patterns.
Thus, Japanese Patent Laid-open No. 2003-230109 proposes a line scanning line interpolation circuit which averages highly-correlative diagonal direction pixel values to prevent the resolution degradation of diagonal edges. In this proposal, in the respective pixels of upper and under lines of the interpolation line, a pair of pixels are used for the interpolation, which is positioned at a point-symmetric point whose center is an interpolation pixel of the interpolation line. The correlation is detected for each of such pair of pixels, and a direction of a pair of pixels whose correlation is highest is decided to be a direction of a pixel (correlation direction) whose correlation is high with respect to the interpolation pixel. Next, the interpolation pixel is generated by using two pixels positioned in the correlation direction.
However, in a pattern part which is relatively slender, diagonal, and line-like, etc., the correlation direction may not be correctly specified. For example, it is assumed that a pair of pixels for specifying the correlation direction is positioned at background parts of both sides crossing over the line-like pattern. In such a case, if the brightness of the background parts is approximately the same, it may be considered that the correlation direction obtained for the interpolation pixel in the line-like pattern is specified as not a direction of the line but a direction of the pair of pixels positioned at the background. If so, the interpolation pixel in the line-like pattern is interpolated by using two pixels of the background, then breaks, unsharpness, jaggy may be induced in the line-like pattern.